#13371: instance selection too eager -------------------------------------+------------------------------------- Reporter: aavogt | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.2 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by niteria): This reproduces on recent HEAD. This appears to be another case of unspoken assumptions about the order. On top of c9bcaf3165586ac214fa694e61c55eb45eb131ab it suffices to make this change: {{{ --- a/compiler/typecheck/TcMType.hs +++ b/compiler/typecheck/TcMType.hs @@ -874,7 +874,7 @@ quantifyZonkedTyVars gbl_tvs (DV{ dv_kvs = dep_tkvs, dv_tvs = nondep_tkvs }) -- closeOverKinds all_cvs: do not quantify over coercion -- variables, or any any tvs that a covar depends on - nondep_tvs = dVarSetElems $ + nondep_tvs = varSetElems . dVarSetToVarSet $ nondep_tkvs `dVarSetMinusVarSet` gbl_tvs -- No worry about dependent covars here; they are -- all in dep_tkvs }}} to make the problem go away. It also fixes the problem on HEAD, except you have to use `nonDetEltsUFM` instead of `varSetElems`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13371#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler